libjava/gnu/java/security/util/Prime.java

   1 /* Prime.java --- Prime number generation utilities
   2    Copyright (C) 1999 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package gnu.java.security.util;
  40 import java.math.BigInteger;
  41 import java.util.Random;
  42 //import java.security.SecureRandom;
  43
  44 public final class Prime
  45 {
  46
  47   /*
  48     See IEEE P1363 A.15.4 (10/05/98 Draft)
  49   */
  50   public static BigInteger generateRandomPrime( int pmin, int pmax, BigInteger f )
  51   {
  52     BigInteger d;
  53
  54     //Step 1 - generate prime
  55     BigInteger p = new BigInteger( (pmax + pmin)/2, new Random() );
  56     if( p.compareTo( BigInteger.valueOf( 1 ).shiftLeft( pmin ) ) <= 0 )
  57       {
  58         p.add( BigInteger.valueOf( 1 ).shiftLeft( pmin ).subtract( p ) );
  59       }
  60
  61     //Step 2 - test for even
  62     if( p.mod( BigInteger.valueOf(2) ).compareTo( BigInteger.valueOf( 0 )) == 0)
  63       p.add( BigInteger.valueOf( 1 ) );
  64
  65     for(;;)
  66       {
  67         //Step 3
  68         if( p.compareTo( BigInteger.valueOf( 1 ).shiftLeft( pmax)) > 0)
  69           {
  70             //Step 3.1
  71             p = p.subtract( BigInteger.valueOf( 1 ).shiftLeft( pmax) );
  72             p = p.add( BigInteger.valueOf( 1 ).shiftLeft( pmin) );
  73             p = p.subtract( BigInteger.valueOf( 1 ) );
  74
  75             //Step 3.2
  76             // put step 2 code here so looping code is cleaner
  77             //Step 2 - test for even
  78             if( p.mod( BigInteger.valueOf(2) ).compareTo( BigInteger.valueOf( 0 )) == 0)
  79               p.add( BigInteger.valueOf( 1 ) );
  80             continue;
  81           }
  82
  83         //Step 4 - compute GCD
  84         d = p.subtract( BigInteger.valueOf(1) );
  85         d = d.gcd( f );
  86
  87         //Step 5 - test d
  88         if( d.compareTo( BigInteger.valueOf( 1 ) ) == 0)
  89           {
  90             //Step 5.1 - test primality
  91             if( p.isProbablePrime( 1 ) == true )
  92               {
  93                                 //Step 5.2;
  94                 return p;
  95               }
  96           }
  97         //Step 6
  98         p = p.add( BigInteger.valueOf( 2 ) );
  99
 100         //Step 7
 101       }
 102   }
 103
 104
 105   /*
 106     See IEEE P1363 A.15.5 (10/05/98 Draft)
 107   */
 108   public static BigInteger generateRandomPrime( BigInteger r, BigInteger a, int pmin, int pmax, BigInteger f )
 109   {
 110     BigInteger d, w;
 111
 112     //Step 1 - generate prime
 113     BigInteger p = new BigInteger( (pmax + pmin)/2, new Random() );
 114
 115   steptwo:{ //Step 2
 116       w = p.mod( r.multiply( BigInteger.valueOf(2) ));
 117
 118       //Step 3
 119       p = p.add( r.multiply( BigInteger.valueOf(2) ) );
 120       p = p.subtract( w );
 121       p = p.add(a);
 122
 123       //Step 4 - test for even
 124       if( p.mod( BigInteger.valueOf(2) ).compareTo( BigInteger.valueOf( 0 )) == 0)
 125         p.add( r );
 126
 127       for(;;)
 128         {
 129           //Step 5
 130           if( p.compareTo( BigInteger.valueOf( 1 ).shiftLeft( pmax)) > 0)
 131             {
 132               //Step 5.1
 133               p = p.subtract( BigInteger.valueOf( 1 ).shiftLeft( pmax) );
 134               p = p.add( BigInteger.valueOf( 1 ).shiftLeft( pmin) );
 135               p = p.subtract( BigInteger.valueOf( 1 ) );
 136
 137               //Step 5.2 - goto to Step 2
 138               break steptwo;
 139             }
 140
 141           //Step 6
 142           d = p.subtract( BigInteger.valueOf(1) );
 143           d = d.gcd( f );
 144
 145           //Step 7 - test d
 146           if( d.compareTo( BigInteger.valueOf( 1 ) ) == 0)
 147             {
 148               //Step 7.1 - test primality
 149               if( p.isProbablePrime( 1 ) == true )
 150                 {
 151                                 //Step 7.2;
 152                   return p;
 153                 }
 154             }
 155           //Step 8
 156           p = p.add( r.multiply( BigInteger.valueOf(2) ) );
 157
 158           //Step 9
 159         }
 160     }
 161     //Should never reach here but makes the compiler happy
 162     return BigInteger.valueOf(0);
 163   }
 164 }